package com.sunyard.utils;

import java.util.Arrays;

public class CrcUtils {
    /**
     * 为Byte数组最后添加两位CRC校验
     *
     * @param buf（验证的byte数组）
     * @return
     */
    public static byte[] setParamCRC(byte[] buf) {
        int checkCode = 0;
        checkCode = crc_16_CCITT_False(buf, buf.length);
        byte[] crcByte = new byte[2];
        crcByte[0] = (byte) ((checkCode >> 8) & 0xff);
        crcByte[1] = (byte) (checkCode & 0xff);
        // 将新生成的byte数组添加到原数据结尾并返回
        return concatAll(buf, crcByte);
    }

    /**
     * 为Byte数组最后添加两位CRC校验
     *
     * @param buf（验证的byte数组）
     * @return
     */
    public static byte[] getCrc(byte[] buf) {
        int checkCode = 0;
        checkCode = crc_16_CCITT_False(buf, buf.length);
        byte[] crcByte = new byte[2];
        crcByte[0] = (byte) ((checkCode >> 8) & 0xff);
        crcByte[1] = (byte) (checkCode & 0xff);
        // 将新生成的byte数组添加到原数据结尾并返回
        return crcByte;
    }

    /**
     * CRC-16/CCITT-FALSE x16+x12+x5+1 算法
     * <p>
     * info
     * Name:CRC-16/CCITT-FAI
     * Width:16
     * Poly:0x1021
     * Init:0xFFFF
     * RefIn:False
     * RefOut:False
     * XorOut:0x0000
     *
     * @param bytes
     * @param length
     * @return
     */
    public static int crc_16_CCITT_False(byte[] bytes, int length) {
        int crc = 0xffff; // initial value
        int polynomial = 0x1021; // poly value
        for (int index = 0; index < bytes.length; index++) {
            byte b = bytes[index];
            for (int i = 0; i < 8; i++) {
                boolean bit = ((b >> (7 - i) & 1) == 1);
                boolean c15 = ((crc >> 15 & 1) == 1);
                crc <<= 1;
                if (c15 ^ bit)
                    crc ^= polynomial;
            }
        }
        crc &= 0xffff;
        //输出String字样的16进制
        String strCrc = Integer.toHexString(crc).toUpperCase();
        System.out.println(strCrc);
        return crc;
    }

    /***
     * CRC校验是否通过
     * @param srcByte
     * @param length(验证码字节长度)
     * @return
     */
    public static boolean isPassCRC(byte[] srcByte, int length) {

        // 取出除crc校验位的其他数组，进行计算，得到CRC校验结果
        int calcCRC = calcCRC(srcByte, 0, srcByte.length - length);
        byte[] bytes = new byte[2];
        bytes[0] = (byte) ((calcCRC >> 8) & 0xff);
        bytes[1] = (byte) (calcCRC & 0xff);

        // 取出CRC校验位，进行计算
        int i = srcByte.length;
        byte[] b = {srcByte[i - 2], srcByte[i - 1]};

        // 比较
        return bytes[0] == b[0] && bytes[1] == b[1];
    }

    /**
     * 对buf中offset以前crcLen长度的字节作crc校验，返回校验结果
     *
     * @param buf
     * @param crcLen
     */
    private static int calcCRC(byte[] buf, int offset, int crcLen) {
        int start = offset;
        int end = offset + crcLen;
        int crc = 0xffff; // initial value
        int polynomial = 0x1021;
        for (int index = start; index < end; index++) {
            byte b = buf[index];
            for (int i = 0; i < 8; i++) {
                boolean bit = ((b >> (7 - i) & 1) == 1);
                boolean c15 = ((crc >> 15 & 1) == 1);
                crc <<= 1;
                if (c15 ^ bit)
                    crc ^= polynomial;
            }
        }
        crc &= 0xffff;
        return crc;
    }

    /**
     * 多个数组合并
     *
     * @param first
     * @param rest
     * @return
     */
    public static byte[] concatAll(byte[] first, byte[]... rest) {
        int totalLength = first.length;
        for (byte[] array : rest) {
            totalLength += array.length;
        }
        byte[] result = Arrays.copyOf(first, totalLength);
        int offset = first.length;
        for (byte[] array : rest) {
            System.arraycopy(array, 0, result, offset, array.length);
            offset += array.length;
        }
        return result;
    }


    static int[] crctab = {0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, 0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, 0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823, 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70, 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f, 0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, 0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634, 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, 0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1, 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0};

    public static short updcrc_ccitt(byte cp, short crc) {

        return (short) ((crc << 8) ^ (short) crctab[((crc >> 8) ^ cp++) & 255]);
    }

    //==========================================================
// 函数名称： CRC16// 函数功能： 计算 CRC16 校验码// 入口参数： cp，数据首地址；leng， 数据长度// 返回参数： crc，计算结果
// 说明：
//==========================================================
    public static byte[] CRC16(byte[] cp) {
        int leng = cp.length;

        int i;
        short crc = 0;
        for (i = 0; i < leng; i++) {

            crc = updcrc_ccitt(cp[i], crc);
        }

        return short2byte(crc);
    }

    public static byte[] short2byte(short s) {
        byte[] b = new byte[2];
        for (int i = 0; i < 2; i++) {
            int offset = 16 - (i + 1) * 8; //因为byte占4个字节，所以要计算偏移量
            b[i] = (byte) ((s >> offset) & 0xff); //把16位分为2个8位进行分别存储
        }
        return b;
    }


}

